208 STUDIES IN GENERAL PHYSIOLOGY 
has thus far been the lower end of the piece, while those substances 
leading to the formation of stems will collect at the upper end. 
Since their flow is stopped here, which would have been impossible 
inthe uninjured plant, they give rise to the roots and stems at the 
corresponding ends. Ina piece of leaf capable of regeneration both 
kinds of formative substances will be moving simultaneously 
toward the basal end to flow toward the stem; stopped 
‘p by the cut surface, they collect there to form stems 
\ y and roots simultaneously. (P. 470.) 
fa Finally, “the different formative substances are 
produced only in limited quantities” (p. 468). 
Corresponding to this theory we assume that 
> there are present in the stems of a Tubularian 
7 re specific substances for the formation of polyps 
which gather at both cut ends and thus bring 
about the formation of polyps. These substances 
must, however, ceteris paribus, collect more 
+k, quickly, or in sufficient amounts, sooner at the 
oral than at the aboral cut end; and the cause of 
wW_ this difference is to be determined by experiment. 
eek 3. It might at first be thought that the specific 
substances necessary for the formation of polyps exist from 
the beginning in greater amount at the oral end of a Tubu- 
larian stem than at the aboral, and that a polyp is, in conse- 
quence, formed more quickly at the oral than at the aboral 
end. To ascertain whether this be true I amputated the 
root and the polyp of Tubularians and cut the remaining 
stem ab (Fig. 53) in half by a transverse incision between ¢ 
and d. All four cut ends were surrounded by water. If 
now the substance necessary for the formation of polyps 
were present in larger amounts in the oral half ac than in 
the aboral piece bd, the former should form polyps sooner 
than the latter. Yet polyps were formed at about the same 
time upon both pieces, only the oral cut ends a and d 
developed polyps much sooner thane and b. I have already 
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